A power supply unit, which is mounted on an electric vehicle, a hybrid vehicle, or the like to supply an electric motor with electricity, is provided by vertically and horizontally arranging a plurality of cell battery assemblies (cell modules), in which a plurality of unit cell batteries are laminated in parallel and also connected to each other in series, and further connecting these assemblies in series. Also, voltage detection wires for detecting voltages of the plurality of unit cell batteries individually are led out from the power supply unit and further connected to an electronic component housing unit (ECU, electrical connection box). Thus, the ECU is adapted so as to detect the voltages of the unit cell batteries and further control the voltage of the power supply unit. The connection of the voltage detection wires to the ECU is accomplished by connecting a connector to respective terminals of the voltage detection wires and subsequently fitting the connector to a mating connector portion provided in the ECU.
Meanwhile, when a vehicle is submerged due to a heavy rain, a flood, or the like, there is a risk that in-vehicle components could be also immersed in water. Particularly, if such an ECU to which the voltage detection wires led out from the power supply unit is submerged, the connector connecting the voltage detection wires to the ECU may be also submerged. Although the incursion of water into the ECU is blocked by a sealed case, there is a risk that water could intrude into the case through the connector.
Therefore, it would be envisaged to construct the connector connecting the voltage detection wires with the ECU as a waterproof connector having a waterproofing property. However, as the waterproof connector requires a waterproof rubber plug, a packing, and the like, the number of components is increased, and furthermore, the manufacturing cost is elevated because a mating connector part on the side of the ECU has to be constructed with a water proof property.
JP 2007-288908 A (PTL 1) proposes a structure where the electrical connection box (ECU) is covered, from the top side in the vehicular vertical direction, with a cover that rise of a water level up to a connecting part of the connector in submergence is prevented by the action of air pressure of a space inside the cover. In this conventional example, as the connecting part with terminals of wires is positioned on the bottom side of the electrical connection box, the structure is adapted so that even if a vehicle submerges, water level would not rise up to the bottom side of the electrical connection box due to air pressure inside the cover. Consequently, even when the electrical connection box is submerged, electronic components are adapted so as to be protected against water.